The disclosures of Japanese Patent Applications No. HEI 11-235947 filed on Aug. 23, 1999 and HEI 11-272804 filed on Sep. 27, 1999 including the specification, drawings and abstract are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a control apparatus of an internal combustion engine, and more particularly, to a control apparatus of an internal combustion engine for controlling an engine speed to a target value during starting of the engine. This invention is also concerned with a method of controlling an internal combustion engine during starting of the engine.
2. Discussion of Related Art
During starting of the engine, and especially, during cold start of the engine, a combustion state is likely to deteriorate, and the engine speed may become unstable. Such deterioration in the combustion state causes problems such as deterioration in engine-starting capability and exhaust properties, and increases in vibration and noise due to the unstable engine speed after starting.
Consequently, various control apparatuses have been proposed for preventing deterioration in the combustion state during starting of the engine so as to stabilize the engine speed. One example of such control apparatuses is described in Japanese Patent Laid-Open Publication No. 62-3139. This control apparatus sets a throttle opening to a target value according to a temperature of the engine cooling water during starting of the engine (the expression xe2x80x9cduring starting of the enginexe2x80x9d as used herein refers to the period from the start of an engine starting operation, or start of cranking, until the engine is brought into a steady idle state after complete explosion in the engine). After the complete explosion in the engine, the control apparatus sets the throttle opening so that the engine speed reaches a target value. Another example of control apparatus is described in Japanese Patent Laid-Open Publication No. 5-222997. This control apparatus feedback-controls the intake air flow rate and ignition timing of the engine so that the engine speed reaches a predetermined target value during an idling operation after the start of the engine, whereby the idle speed is maintained at a constant value.
If the engine speed is controlled only by adjusting the throttle opening during starting of the engine, as in the control apparatus of the above-mentioned Japanese Patent Laid-Open Publication No. 62-3139, deterioration of the combustion state in the engine cannot be suppressed, but, on the contrary, may be increased. In an engine having a fuel injection valve for injecting fuel into an inlet port of the engine, for example, the fuel injected during cold start of the engine may adhere to a wall of the inlet port in a liquid form, i.e., without being vaporized. Therefore, the mixture may not have a sufficient concentration of vaporized fuel, with the result that the mixture has a lean air-fuel ratio, and the engine operates in a poor combustion state. In such a case, if the throttle opening is increased, a negative pressure of an inlet pipe downstream of the throttle valve is reduced (i.e., an absolute pressure is increased). As a result, the fuel deposited on the wall becomes less likely to be vaporized, whereby the combustion state is further deteriorated. Thus, by adjusting only the throttle opening, the engine speed may not be accurately controlled to the target value during starting of the engine.
In order to solve the above-mentioned problems, a further example of control apparatus has been proposed, which controls the engine speed during starting of the engine by adjusting a throttle opening (i.e., an intake air flow rate of the engine), and switching the engine speed control through adjustment of the throttle opening to engine speed control through adjustment of the ignition timing when the combustion state in the engine is deteriorated.
The control apparatus as described just above is adapted to determine deterioration of the combustion state based on the peak engine speed, fluctuations in the engine speed, or the like, during starting of the engine. When determining that the combustion state is deteriorated, the control apparatus starts performing engine speed control by adjusting the ignition timing, or increasing the fuel injection amount, instead of adjusting the throttle opening, so as to prevent deterioration in the combustion state. In this way, deterioration in the combustion state is suppressed. It should be noted that, hereinafter, controlling the engine speed by adjusting the throttle opening will be simply referred to as xe2x80x9cthrottle valve controlxe2x80x9d or xe2x80x9cintake air flow controlxe2x80x9d; controlling the engine speed by adjusting the ignition timing of the engine will be simply referred to as xe2x80x9cignition timing controlxe2x80x9d; and controlling the engine speed by increasing the fuel injection quantity will be simply referred to as xe2x80x9cfuel injection quantity control.xe2x80x9d
As a result of subsequent studies, it was reveled that the control apparatus as described above switches the engine speed control from the throttle valve control to the ignition timing control or injection quantity control as soon as it determines a poor combustion state in the engine, and that a favorable result cannot always be obtained in terms of maintaining an excellent exhaust properties.
For example, during starting of the engine, the ignition timing of the engine is generally delayed with respect to that during normal operations, in order to increase an exhaust temperature and quickly raise a temperature of an exhaust purifying catalyst disposed in an exhaust passage to a catalyst-activating temperature. However, if the control apparatus switches the engine speed control from the throttle valve (intake air flow rate) control to the ignition timing control, the ignition timing of the engine is advanced with respect to that during the normal starting. As a result, the exhaust temperature is reduced, and the temperature rise of the catalyst is delayed. Accordingly, if the engine speed control is performed by adjusting the ignition timing during starting of the engine, warm-up of the catalyst is delayed, and the engine is operated for a long time without sufficiently purifying the exhaust. In addition, when the engine speed control is switched from the throttle valve control to the injection quantity control, the amount of unburned components HC and CO in the exhaust is increased, and the exhaust properties are thus degraded. Therefore, in controlling the engine speed during starting of the engine, it is preferable to maintain the throttle valve control as long as possible without switching to the ignition timing or fuel injection quantity control. However, the control apparatus as described above switches to the ignition time or injection quantity control as soon as the combustion state is deteriorated. Such switching may possibly degrade the exhaust properties even if the deterioration in the combustion state could be suppressed only by the throttle valve control.
Moreover, in the control apparatus as described above, the timing of starting the engine speed control during starting of the engine is not sufficiently considered. For example, after the engine starting operation (cranking) is started, the engine speed rapidly increases when combustion is started in all cylinders of the engine. Then, the engine speed reaches a peak value, and is then reduced down to a constant value. During starting of the engine, the engine speed needs to be controlled so that it quickly settles or converges at a predetermined target value. However, with the engine speed changing as described above after the engine starting operation is started, the time required for the engine speed to be settled at the target value after the engine starting operation is started depending upon the timing of starting the engine speed control.
As described above, the control apparatus as described above switches from the intake air flow control to the ignition timing control depending upon whether the engine is operation in a poor combustion state or not. However, the time required for the engine speed to be settled at the target value may be increased depending upon a method of controlling the engine speed by adjusting ignition timing after the switching.
It is therefore a first object of the present invention to provide a control apparatus for an internal combustion engine, which is capable of accurately maintaining the engine speed at a target value while effectively suppressing deterioration in the combustion state during starting of the engine, and is also capable of suppressing degradation in exhaust properties during starting of the engine.
It is a second object of the present invention to provide a control apparatus of an internal combustion engine, which is capable of quickly settling the engine speed at a target value during starting of the engine.
To accomplish the first object, a control apparatus for an internal combustion engine is provided according to the first aspect of the present invention, which apparatus controls an engine speed to a target value during starting of the engine, by performing at least one control including intake air flow control under which an intake air flow rate is adjusted in accordance with the engine speed, and ignition timing control under which the ignition timing is adjusted in accordance with the engine speed, and comprises: a parameter acquiring unit that obtains a parameter that represents a degree of deterioration of a combustion state in the engine; and a switching unit that control switching from the intake air flow control to the ignition timing control based on the parameter obtained in said calculating unit.
In the control apparatus as described above, the parameter acquiring unit may calculate a difference between a predetermined reference peak engine speed and an actual peak engine speed during starting of the engine, to provide the parameter, and the switching unit may switch from the intake air flow control to the ignition timing control, depending upon the difference between the peak engine speeds.
Where the combustion state in the engine is deteriorated, the peak engine speed during starting of the engine is reduced, and therefore a difference between the reference peak engine speed and the peak engine speed increases in accordance with the deterioration of the combustion state. The reference peak engine speed is set to a standard peak engine speed achieved where the combustion state is not deteriorated, and a difference between the peak engine speeds is set in advance for the case where the combustion state is most deteriorated in a range in which the engine speed can be controlled by the intake air flow control. If the actual difference between the peak engine speeds becomes larger than the difference thus set in advance, the intake air flow control is switched to the ignition timing control, thus preventing unnecessary switching to the ignition timing control. With this arrangement, the intake air flow control is performed as long as possible even during poor combustion in the engine, thus preventing deterioration of the exhaust properties.
To accomplish the second object, a control apparatus for an internal combustion engine is provided according to a second aspect of the present invention, which performs engine speed control for controlling an engine speed to a predetermined target value in a feedback manner during starting of the engine, and comprises: an integrating unit that integrates an intake air quantity that has been introduced into the engine since the start of an engine starting operation; and a control unit that starts the engine speed control when an integrated value of the intake air quantity calculated by the integrating unit reaches a value that is equal to a volume of an intake air passage that extends from a throttle valve to an inlet of each cylinder.
In the control apparatus as described above, the engine speed feedback control during starting of the engine is started at a point of time when the integrated value of the intake air quantity becomes equal to a volume of the intake air passage disposed downstream of the throttle valve, namely, at a point of time when the entire amount of the air retained in the intake passage downstream of the throttle valve is sucked or introduced into the engine upon start of the engine. In general, the engine speed control needs to be started as soon as possible so that the engine speed is settled at the target value in a short period of time. At the time of starting the engine, however, the air held at an atmospheric pressure is stored in the intake air passage downstream of the throttle valve, and the air thus stored downstream of the throttle valve is introduced into the engine irrespective of the throttle opening once an engine start operation is started. Namely, the intake air quantity or flow rate cannot be accurately controlled during this period even if the throttle opening is changed, and therefore the engine speed cannot be controlled by adjusting, for example, the intake air flow rate. According to the present invention, the engine speed control is immediately started at a point of time when the entire amount of the air in the intake passage downstream of the throttle valve has been introduced into the engine, namely, when it becomes possible to perform accurate engine speed control. With this arrangement, the engine speed during starting of the engine settles or converges at the target engine speed in a short time.